The present invention relates to a device using a differential amplifier made in CMOS monolithic IC form and to a differential amplifier made in CMOS monolithic IC form.
One example of a conventional CMOS differential amplifier is shown in FIG. 2.
A differential amplifying stage 101 has input transistors 1, 2 transistors 3, 4 forming a current mirror stage, resistors 8, 9 a constant current source 6, and an output thereof is connected to a gate of an output transistor 5 to directly drive the output transistor 5. When a gate voltage of a non-inverted input transistor 2 is higher than a gate voltage of an inverted input transistor 1, a drain voltage of the output transistor 5 as a differential amplifier output becomes high in voltage value. When the gate voltage of the non-inverted input transistor 2 is lower than a gate voltage of the inverted input transistor 1, the drain voltage of the output transistor 5 as the differential amplifier output becomes low in voltage value.
The differential amplifier formed by a CMOS element has an input offset voltage generally of approximately .+-.10 mV at maximum, whereas the differential amplifier formed by a bipolar element has an input offset voltage generally of approximately .+-.5 mV at maximum. Thus the input offset voltage of the differential amplifier formed by a CMOS element is worse in input offset voltage than that formed by a bipolar element.
In using a CMOS element, an improvement in input offset voltage of the differential amplifier can be achieved by trimming the resistances 8, 9 or other elements in FIG. 2 using a laser or the like on the chip. This however requires on-chip occupying portions thus resulting in chip size increase.
There has been a problem in that both the trimming process addition and the chip size increase constitute a factor of increased cost.
Also, the CMOS differential amplifier improved in input offset voltage by utilizing laser trimming is large in chip size and hence large in package size, and is thus not suited for mounting on small apparatuses such as portable apparatuses.